where is the secondary motor cortex

Secondary Motor Cortex: Where 'Sensory' Meets 'Motor' in the Rodent Frontal Cortex In rodents, the medial aspect of the secondary motor cortex (M2) is known by other names, including medial agranular cortex (AGm), medial precentral cortex (PrCm), and frontal orienting field (FOF).

Full Answer

What happens if you damage your primary motor cortex?

When an injury damages the primary motor cortex, the person will typically present with poor coordination of movements and poor dexterity. For example, the person usually loses the ability to perform fine motor movements. Fine motor movements involve the muscles of the hands, fingers, and wrists.

What does primary motor cortex mean?

The primary motor cortex is a strip of brain tissue located in the frontal lobe. It is responsible for initiating purposeful movements. These purposeful movements include everything from moving your hands, arms, and legs to controlling facial expressions and even swallowing motions.

Is the cerebral cortex and the motor cortex the same?

The motor cortex is associated with the movement of body parts while the sensory cortex (auditory cortex, visual cortex etc.,) is associated with sensory organs. There is a portion of the cerebral cortex which is not occupied by motor and sensory cortices, known as the ‘association cortex’.

What does a motor cortex control?

The motor cortex of the brain is a region in the posterior part of the frontal lobe that controls voluntary movement. Neurons in this region of the brain send signals down the spinal cord to the muscles to coordinate movements.

Where is the secondary motor cortex located in the brain?

frontal lobeWhere is the motor cortex? Motor cortex (in red). The motor cortex is found in the frontal lobe, spreading across an area of cortex situated just anterior to a large sulcus known as the central sulcus, which runs down the side of the cerebral hemispheres.

What is secondary motor cortex?

The secondary motor cortex (M2) is a prime candidate for this role given its interconnectivity with association cortices that encode spatial relationships and its projection to the primary motor cortex.

Where is the secondary motor areas?

superior frontal gyrusThe supplementary motor area (SMA) occupies the posterior one third of the superior frontal gyrus and is responsible for planning of complex movements of contralateral extremities but ipsilateral planning to a small effect.

What is the secondary motor area?

Definition. Motor areas of the cerebral cortex, other than primary motor cortex, located in the frontal lobe. These areas all contain corticospinal neurons and make synaptic connections with primary motor cortex.

Where is the primary motor cortex located?

precentral gyrusThe primary motor cortex is located in the precentral gyrus; the premotor area is more rostral. The pyramidal cells of cortical layer V (also called Betz cells) are the upper motor neurons of the primary motor cortex.

What are the 4 motor areas of the cerebral cortex?

The most intensively studied motor areas, the premotor area (PMA), supplementary motor area (SMA), and primary motor cortex (MI), appear to have different roles in movement. PMA is involved in coupling arbitrary cues to motor acts, whereas SMA appears to participate more in internal guidance or planning of movement.

Is motor cortex in frontal lobe?

The primary function of the motor cortex is to generate signals to direct the movement of the body. It is part of the frontal lobe and is anterior to the central sulcus.

Where is the pre supplementary motor area?

dorsomedial frontal cortex3The supplementary motor area (SMA) and pre-supplementary motor area (pre-SMA) are, in humans, located on the medial aspect of the brain: in the dorsomedial frontal cortex3,14, anterior to the leg representation of the primary motor cortex (Fig. 1).

Is the motor cortex in the parietal lobe?

Thus, the primary motor cortex, in the posterior portion of the frontal lobe, is immediately adjacent to the somatosensory cortex, in the anterior portion of the parietal lobe.

What body parts does the motor cortex control?

So, for instance, a large proportion of the motor cortex is devoted to our thumb, fingers, mouth and lips, as they are vital for manipulating objects and speech articulation. The connection from the primary motor cortex to muscles of the body is so important that any damage leads to an impaired ability to move.

What is the motor cortex responsible for?

The primary function of the motor cortex is to generate signals to direct the movement of the body. It is part of the frontal lobe and is anterior to the central sulcus. It consists of the primary motor cortex, premotor cortex, and the supplementary motor area.

What is the primary motor cortex?

The primary motor cortex, located just in front of the central sulcus, is the area that provides the most important signal for the production of skilled movements. Electrical stimulation of this area results in focal movements of muscle groups on the opposite side of the body, depending on the area stimulated.

What does the motor cortex do examples?

Primary motor cortex encodes the direction of movement. Many neurons in the primary motor cortex are selective for a particular direction of movement. For example, one cell may fire strongly when the hand is moved to the left, whereas it will be inhibited when the hand is moved to the right (Figure 3.8).

What happens if the motor cortex is damaged?

When an injury damages the primary motor cortex, the person will typically experience a loss of coordination and poor dexterity. For example, the person usually loses the ability to perform fine motor movements that involve the muscles of the hands, fingers, and wrists.

What are the components of the motor cortex?

Components of the motor cortex. The motor cortex can be divided into three areas: 1. The primary motor cortex is the main contributor to generating neural impulses that pass down to the spinal cord and control the execution of movement. However, some of the other motor areas in the brain also play a role in this function.

Which part of the brain is directly against the motor cortex?

The primary somatosensory cortex, especially the part called area 3a, which lies directly against the motor cortex, is sometimes considered to be functionally part of the motor control circuitry.

What is the difference between area 4 and area 6?

In his view both were part of the same map, though area 6 tended to emphasize the muscles of the back and neck. Woolsey who studied the motor map in monkeys also believed there was no distinction between primary motor and premotor. M1 was the name for the proposed single map that encompassed both the primary motor cortex and the premotor cortex. Although sometimes "M1" and "primary motor cortex" are used interchangeably, strictly speaking, they derive from different conceptions of motor cortex organization.

Which part of the brain is responsible for the preparation of movement?

2. The premotor cortex is responsible for some aspects of motor control, possibly including the preparation for movement, the sensory guidance of movement, the spatial guidance of reaching, or the direct control of some movements with an emphasis on control of proximal and trunk muscles of the body.

Why are the motor cortex and thumbs important?

Enhancements to the motor cortex (and the presence of opposable thumbs and stereoscopic vision ) were evolutionarily selected to prevent primates from making mistakes in the dangerous motor skill of leaping between tree branches (Cartmill, 1974; Silcox, 2007). As a result of this pressure, the motor system of arboreal primates has a disproportionate degree of somatotopic representation of the hands and feet, which is essential for grasping (Nambu, 2011; Pons et al., 1985; Gentilucci et al., 1988).

How did mammals develop their brains?

These early mammals developed several novel brain functions most likely due to the novel sensory processes that were necessary for the nocturnal niche that these mammals occupied. These animals most likely had a somatomotor cortex, where somatosensory information and motor information were processed in the same cortical region. This allowed for the acquisition of only simple motor skills, such as quadrupedal locomotion and striking of predators or prey. Placental mammals evolved a discrete motor cortex about 100 mya. According to the principle of proper mass, "the mass of neural tissue controlling a particular function is appropriate to the amount of information processing involved in performing the function. " This suggests that the development of a discrete motor cortex was advantageous for placental mammals, and the motor skills that these organisms acquired were more complex than their early-mammalian ancestors. Further, this motor cortex was necessary for the arboreal lifestyles of our primate ancestors.

How do motor neurons control movement?

A simple view, that is almost certainly too limited and that dates back to the earliest work on the motor cortex, is that neurons in the motor cortex control movement by a feed-forward direct pathway. In that view, a neuron in the motor cortex sends an axon or projection to the spinal cord and forms a synapse on a motor neuron. The motor neuron sends an electrical impulse to a muscle. When the neuron in the cortex becomes active, it causes a muscle contraction. The greater the activity in the motor cortex, the stronger the muscle force. Each point in the motor cortex controls a muscle or a small group of related muscles. This description is only partly correct.

Where is the motor cortex located?

The motor cortex is situated within the frontal lobe of the brain, next to a large sulcus called the central sulcus. The central sulcus is a groove which runs down the side of the cerebral hemispheres between the frontal and parietal lobes.

What is the primary motor cortex?

The primary motor cortex is a region of the motor cortex which is important for initiating motor movements. The areas of the primary motor cortex correspond precisely to specific body parts.

What is the motor homunculus?

The motor homunculus is a representation of the body parts along the primary motor cortex, or precentral gyrus. Each part of the body that is able to move is represented along this gyrus in an anatomical fashion, representing the contralateral side of the body.

What are the two areas of the nonprimary motor cortex?

The nonprimary motor cortex is further divided into two areas: the premotor cortex and the supplementary motor cortex. The premotor cortex is thought to be involved in planning and executing motor movements.

What causes the motor cortex to be damaged?

Damage to this area may result in dysfunctions associated with the pyramidal neurons, a condition known as upper motor neuron disease.

What is the motor cortex?

The motor cortex is an area within the cerebral cortex of the brain that is involved in the planning, control, and execution of voluntary movements. The motor cortex can be divided into the primary motor cortex and the nonprimary motor cortex.

What is the role of the supplementary motor cortex in the movement of a person?

The supplementary motor cortex is thought to be critical to the execution of sequences of movement, the execution of motor skills, and the control of movement. This can involve taking a role in making a decision to change to a different movement based on sensory input.

What is the function of the nonprimary motor cortex?

Several theories have been put forth regarding the function of the nonprimary motor cortex, particularly in support of skilled movements, motor sequences, and sensory-guided actions 89, 91, 92 . Mechanistically, the brain region may subserve specific functions within the scheme of action preparation, such as the programming of motor acts, limb stabilization, and suppression of default motor response plans [91]. Specifically for premotor and supplementary motor areas, they may have distinct roles in mediating externally instructed versus internally guided actions, or temporal versus spatial sequences of movements [89]. Aside from motor planning and selection, it has also been postulated that premotor functions could occur concomitantly with the allocation of attention 93, 94.

What is the theory of higher order motor cortex?

Theories of Higher-Order Motor Cortex Function. There is a rich history of frontal cortex studies in humans and nonhuman primates. As early as 1935, Fulton ablated parts of the nonprimary motor cortex and noted ‘disorganization of the more highly integrated voluntary movements’ in his subjects [86].

How does microstimulation work?

In microstimulation studies, an electrical current is injected into the brain tissue to evoke movements. By systematically moving the electrode, a motor map may be generated. In primates, such maps have greatly expanded our understanding of frontal cortex organization [27]. For rat M2, large-amplitude currents are needed to elicit any response, consistent with the presence of a nonprimary motor area [4]. When sufficient current is injected, microstimulation leads to a combination of eye, eyelid, vibrissa, and head movements 4, 28. In particular, for vibrissae, the evoked whisker movements may be ipsilateral, contralateral, or bilateral; moreover, multiple whiskers move in concert, arguing against a topographical representation [7]. A similar combination of vibrissa, neck, and head movements could be evoked by intracortical microstimulation of the medial frontal cortex in C57BL/6 mice [29]. The broad combination of evoked movements may be characterized as orienting.

Why are VM1 and M2 different?

This may be partly due to the wide range of stimulation parameters and choice of anesthetic agents . Another possible explanation is that vM1 may have subdivisions, and the anterior portion corresponds to M2. This argument comes from a couple of reports showing that rhythmic whisking may be evoked in posterior vM1, whereas nonrhythmic whisker movements accompanied by complex face, eye, eyelid, and nose movements are associated with stimulating an anterior ‘retraction-face’ subregion of vM1 33, 34. Alternatively, voltage-sensitive dye imaging of neural responses to visual versus whisker stimulation indicated differences along the medial-lateral axis 108, 109. These may be overlapping subdivisions, rather than distinct modules, in the rodent medial frontal cortex. Finally, although it is generally thought that vM1 is involved in whisking behavior, there is no consensus on its function 35, 36.

What is the most medial and dorsal portion of the frontal cortex?

In the literature, the same location in the brain has been called the shoulder region, AGm, PrCm, FOF, M2 (or MOs), dorsomedia l PFC (dmPFC), and second frontal area (Fr2). Moreover, the region may overlap with the vibrissa motor cortex (vM1).

What is M2 imaging?

Given that M2 lies on the dorsal surface of the brain, it is amenable to subcellular-resolution optical imaging. As such, M2 appears to be an ideal platform for characterizing structural plasticity in the mPFC. Taking this approach, the turnover of dendritic spines and axonal boutons in the frontal cortex has been studied in response to cocaine administration [103], activation of dopaminergic neurons [104], fear conditioning [105], and rule learning [106]. Specific to stress-related disorders, the fast-acting antidepressant ketamine exerts longitudinal effects on structural plasticity in M2 [107]. Namely, a single, subanesthetic dose of ketamine leads to a prolonged increase in spine density, which is primarily driven by an elevated rate of spine formation. These results demonstrate the potential of using M2 as a platform to study rodent models of mental illnesses.

What is the function of choice-related activity in M2?

They found that, within the auditory cortex, inputs from M2 primarily have a suppressive effect on firing rates via feedforward inhibition [24]. During locomotion, this pathway was active and contributed to the movement-related suppression of sensory-evoked cortical activity, leading to the idea that M2 provides the corollary discharge to facilitate dynamic adjustment of auditory perception during active behavior [67]. To what extent this potential function of M2 applies to task-specific situation remains to be determined.

What is the effector of M2 neurons?

The activity of M2 neurons is modulated by specifics of the task. One factor is the effector. M2 neurons displayed different firing patterns when the operant action was changed from

What is the role of M2 in the neural circuit?

Such a view positions M2 as a critical node in the neural circuitry for the flexible control of voluntary actions.

What is M2 in a rodent?

M2 is a subdivision of the rodent mPFC (Box 1). As expected for an association region, M2 receives inputs from numerous cortical and thalamic sources. Thalamic projections originate from multiple nuclei [9]. Cortical afferents come from visual, somatosensory, auditory, parietal, retrosplenial, and orbital areas [8,10–12]. Multiple types of cortical input overlap spatially. Still unknown is whether there is any topographical organization of the afferents. It has been suggested that rostral M2 receives more somatic sensorimotor inputs, whereas caudal M2 receivesmoresensoryinputs[10,13].Theremayalsoberegionaldifferences:unlikeCg1,which primarily receives afferents from visual areas, M2 has auditory inputs in addition to visual afferents and, therefore, may be multimodal [14].

What is the M2 efferent connection?

M2 has several notable efferent connections to brain regions associated with motor control. M2 projectsalongthecorticospinaltracttothespinalcord[4,18].Italsosendsaxonstothesuperior colliculus[19]andsubcorticalnucleiinvolvedinoculomotorcontrol[20,21].Terminalfieldsinthe striatumareinhomogeneous,centeringonthedorsocentralpartofthecaudate-putamen[9,22]. This is more lateral than terminal fields from Cg1, consistent with the general medial-lateral organizationoftherodentmPFC-striatalnetwork[22].Intriguingly,inthestriatum,terminalsfrom M2 overlap with those from the posterior parietal cortex (PPC) in both rats and mice [9,23]. This overlap in corticostriatal targeting is in addition to the direct reciprocal connections between M2 and PPC [8]. To add to the complexity, the retrosplenial cortex connects to both M2 and PPC [12], indicating multiple pathways mediating the interactions between these three association cortical regions.

How is a motor map generated?

In microstimulation studies, an electrical current is injected into the brain tissue to evoke movements. By systematically moving the electrode, a motor map may be generated. In primates, such maps have greatly expanded our understanding of frontal cortex organization [27]. For rat M2, large-amplitude currents are needed to elicit any response, consistent with the

What is the function of M2?

Progress is fueled by accessibility of the region for optical imaging and optogenetics, as well as the development of sophis- ticated decision-making tasks for rodents. M2 receives sensory information from reciprocalconnectionswithsensory,par- ietal, and retrosplenial cortices. It exerts control on actions by projecting to var- ious motor-related subcortical regions. RemovalofM2causestransientneglect and enduring sensorimotor deficits. M2 neurons have early and context- dependent choice-related activity, implicating the region as a driver of voluntary actions. Collectively, the current understanding suggests that M2 maintains a flexible mapping diagram of sensorimotor asso- ciations in the service of adaptive choice behavior.

Does VM1 overlap with M2?

Conflicting results come from microstimulation studies of vM1. Electrode track reconstructions suggest that vM1 potentially overlaps with M2 [5]. However, opposite to the aforementioned findings for M2, electrical microstimulation of vM1 causes predominantly whisker movements [30,31].Theevokedmovementsaretopographical,showingwhisker-by-whiskerrepresentation asafunctionofdepthinthecortex.BasedsolelyontheresultsfromvM1,thestimulatedregions should be considered as the vibrissa representation of the primary motor cortex, rather than a nonprimary motor area.

What is the function of the secondary motor cortex?

The secondary motor cortex (M2) in rodents is a homolog of the premotor cortex, supplementary motor area, or frontal eye field in monkey (Barthas and Kwan, 2017; Reep et al., 1987; Svoboda and Li, 2018; Zingg et al., 2014). M2 plays a critical role in the flexible control of voluntary action (Barthas and Kwan, 2017; Ebbesen et al., 2018). Removal or inactivation of M2 caused deficits in cue-guided actions (Barthas and Kwan, 2017; Erlich et al., 2015; Passingham et al., 1988), and an increase in errors during behavioral switch from nonconditional responding to cue-guided actions (Siniscalchi et al., 2016). M2 neurons exhibited choice-related activity, which is earlier than that in other frontal cortical regions (Sul et al., 2011). Neural signals in M2 also conveyed information about past choice and outcome (Hattori et al., 2019; Jiang et al., 2019; Scott et al., 2017; Siniscalchi et al., 2019; Sul et al., 2011; Yuan et al., 2015). The findings in these previous studies raise the possibility that M2 may be important for adaptive action selection during flexible stimulus categorization. Furthermore, it would be interesting to elucidate whether the choice- and history-related signals in M2 are modulated by the task demand to remap stimulus-action association.

Which cortical regions are involved in flexible behavior?

Prefrontal cortical regions, including the medial prefrontal cortex (mPFC) and the orbitofrontal cortex (OFC), have been implicated in flexible behavior (Birrell and Brown, 2000; Dias et al., 1996; Duan et al., 2015; Floresco et al., 2006; Izquierdo et al., 2017; Ragozzino, 2007; Ragozzino et al., 1999; Stefani et al., 2003). We thus also examined the role of prefrontal cortex in the flexible visual categorization task. We found that bilateral inactivation of mPFC or OFC did not cause significant change in the performance for the reversing stimulus, the distance between internal categorical boundaries or number of switches per session (p>0.05, Wilcoxon signed rank test, mPFC: n = 13 mice, OFC: n = 9 mice, Figure 4—figure supplement 6and Figure 4—figure supplement 7), although OFC inactivation tended to increase the number of trials per block (Figure 4—figure supplement 7). Inactivation of mPFC or OFC did not affect the parameters in the dynamic-DC model (Figure 4—figure supplement 6and Figure 4—figure supplement 7). Thus, the impaired performance for the reversing stimulus during the switching period was specific to M2 inactivation.

Which neurons encode information about choice and sensory history?

Information about choice and sensory history encoded by M2 neurons

Which part of the brain is responsible for flexible action selection during stimulus categorization?

The secondary motor cortex causally contributes to flexible action selection during stimulus categorization with the representations of upcoming choice and sensory history regulated by the demand to remap stimulus–action association.

Which brain regions have flexible stimulus categories?

Neural representation of stimulus category has been found in lateral intraparietal cortex (Freedman and Assad, 2006), prefrontal cortex (Freedman et al., 2001) and medial premotor cortex (Romo et al., 1997). Neural correlates of flexible stimulus categorization are found in monkey pre-supplementary motor cortex (Mendoza et al., 2018) and the frontal eye field (Ferrera et al., 2009). Neurons in monkey prefrontal and anterior cingulate cortex also showed dynamic task selectivity in task switching that requires flexible adjustment of behavior (Johnston et al., 2007). However, the causal role of frontal and premotor regions in the performance of flexible stimulus categorization remains to be investigated.

Overview

The motor cortex is the region of the cerebral cortex involved in the planning, control, and execution of voluntary movements. Classically, the motor cortex is an area of the frontal lobe located in the posterior precentral gyrus immediately anterior to the central sulcus.

Components of the motor cortex

History

The motor cortex map

Evolution of the motor cortex

See also

Further reading

External links